Spatial light modulators, including particularly liquid crystal displays (LCDs), often use a backlight or a frontlight to provide light for the display. A common light source for these lights are light emitting diodes (LEDs), with the LEDs either being directly underneath the LCD (so-called direct lit) or illuminating the edge of a waveguide disposed below the LCD (so-called edge lit), or a combination of the two. An example of a combination is where the backlight is made of an array of LEDs illuminating a waveguide, where the waveguides are tiled to form a backlight.
Optical waveguides can be either flat sheets or can be tapered, and may have edges that are coated with a reflective material, such as a metallic tape. The waveguides are commonly manufactured by molding or casting of resin into the near-final or final shape, or are fabricated from a larger sheet.